Gallium arsenide substrates are frequently utilized when forming devices with III-V materials because these substrates allow III-V films to be grown epitaxially in a lattice-matched manner and thus with few defects. Nevertheless, gallium arsenide substrates are expensive, and it is frequently not cost effective to utilize such substrates only one time. Epitaxial lift-off (ELO) is one processing scheme that allows a gallium arsenide substrate to be used several times. In a typical ELO process, a thin sacrificial aluminum arsenide layer is grown on a gallium arsenide growth substrate, and then several III-V thin films are epitaxially grown on the sacrificial aluminum arsenide layer to produce a device layer. The device layer is then further processed to form the desired devices. With the devices formed, reuse of the gallium arsenide growth substrate is afforded by selectively etching away the aluminum arsenide sacrificial layer in hydrofluoric acid so as to undercut the device layer and allow it to be lifted away. The liberated device layer may then be re-attached to some other substrate, which need no longer be a substrate capable of supporting epitaxial III-V growth. The original gallium arsenide growth substrate is left intact and undamaged, and available for reuse.
Nevertheless, despite their promise, ELO processes may suffer from several disadvantages. For example, when etching the sacrificial layer to lift off the device layer from the growth substrate, it is often necessary to create curvature in the sample in order to allow a reasonable lateral diffusion rate of etchant to the etching front and to prevent the etching from stopping due to the buildup of gaseous byproducts from the etching process. Such curvature may, for example, be induced by the use of weights or wax forms. However, these methods of adding curvature tend to require that each wafer be set up individually; that is, they are manual, single-wafer solutions. Throughput is low, and attention is required during wet etching.